Many telecommunication systems are available for connecting terminal equipment to switched circuit and packet data networks. Most provide communication services to terminals, or end systems that reside in a fixed location, connecting to a network at a topologically restricted point in order to facilitate static routing of packets or calls, for instance fixed telephone or local area networks. Mobility features have been designed into cellular equipment, to support connection of a mobile terminal or end system to a cellular basestation depending on the geographic area covered by the basestation and the radio path between the basestations and the mobile end system. Cellular systems have been designed to provide switched circuit communications, for cellular telephones as defined in TIA RS-553 specifications, and more recently in cellular packet data communications, as defined in the CDPD specifications.
Interworking requirements for fixed and cellular telephone equipment have been developed to provide uniform service, including a uniform numbering plan and compatible call setup procedures. The North American cellular industry has developed the RS-553, IS-54, and IS-41 specifications for switching systems to allow cellular telephones to roam between cellular switch systems, providing authentication, location tracking, call routing and setup, and handoff between cellular switch systems. Similar specifications have been developed for other cellular systems including European GSM.
Similarly, interworking requirements for fixed and cellular packet data systems have been developed to provide uniform service, with a uniform addressing plan and compatible packet transport procedures. Packet data networks may include equipment to facilitate the operation of interconnected subnetworks using different communications technologies. The Internet protocol stack for TCP/IP communications defines communications methods that permits different technologies such as Ethernet, X.25, satellite, and dialup circuits to interoperate. Packet data networks can include switched circuit data links using modems and asynchronous communications equipment with X.25 protocol capabilities, or asynchronous communication using the Internet SLIP or PPP protocols. The cellular industry has developed the CDPD specifications for cellular digital packet data communications to allow mobile end systems to roam between cellular packet data systems while providing effective packet data communication services.
A cellular telephone system provides circuit-switched radio communication between a stationary cellular switch system and one or more cellular telephones, and other equipment accessible through the switched telephone network. Circuit-switched radio communication is typically used to provide voice, facsimile, and data communication services. The cellular switch system typically includes equipment for interconnecting to the switched telephone network, a network of geographically separated circuit basestations, circuit-switching equipment for connecting the telephone network to the basestations, circuit control equipment, and other equipment over radio links, where a call is established between a mobile end system and a basestation. Such a cellular telephone system is described in the Bell System Technical Journal, January 1979, entitled, "The Cellular Concept," page 15, et seq.
Cellular switch systems provide mobile telephone service to cellular telephones in the geographic areas covered by the basestations. Cellular switch systems are interconnected by trunking facilities that provide circuit-switched communication paths between base systems, either directly or through the switched telephone network.
Cellular telephones are mobile, and may roam between geographic areas covered by circuit basestations that are part of different cellular switch systems. Intersystem signalling procedures following the IS-41 standards between cellular switch systems is supported by data communication networks that communicate information about the identity, location, and capabilities of roaming cellular telephones between the control equipment at different cellular switch systems. This information is used to provide circuit-switched communication between cellular telephones or cellular mobile end systems, without constraining such service to the geographic area covered by a single cellular switch system.
A cellular packet data system provides packet data radio communication between a stationary cellular packet data system and one or more cellular packet mobile end systems. Packet data radio communication provides data communication between fixed end systems and mobile end systems, or between mobile end systems and other mobile end systems. A cellular packet data system typically includes equipment for interconnecting to one or more packet data networks, a network of geographically separated packet basestations, packet switching equipment, and other equipment. A cellular packet data system uses one or more radio channels that are shared by several mobile end systems, for transmission of data in bursts between the mobile end systems and a basestation. Interconnection to fixed packet data networks may be provided over various suitable communication media.
Cellular packet mobile end systems are typically portable, and may roam between geographic areas covered by packet basestations that are part of different cellular packet data systems. Data communication between cellular packet data systems communicates information about the identity, location, and capabilities of roaming packet mobile end systems between data switches at different cellular packet data systems. This information is used to provide data communication to cellular packet mobile end systems, without constraining such service to the geographic area covered by a single cellular packet data system.
A cellular packet data system may operate independent of any cellular switch system, or may interconnect with the cellular telephone system to share common equipment or resources, e.g., radio channel assignment, antennae or telephone interface equipment. One method of interconnecting a cellular telephone system and a cellular packet data system is described in U.S. patent application Ser. No. 07/674,660, filed Mar. 25, 1991, now abandoned.
One weakness of the current cellular switch system and cellular packet data system technology is the inability to provide packet data coverage to mobile end systems outside of the area of coverage of the cellular packet data system. It is desired to use switched circuit cellular equipment to provide an alternate means of access to packet data networks, in areas not covered by cellular packet data systems, or to use fixed telephone circuits or local area network interfaces where neither cellular nor cellular packet coverage is available. Current switching equipment cannot offer solutions to these requirements.
A cellular remote unit may operate independent of any packet remote unit, or the two remotes may be integrated to share common equipment or resources. Typically, circuit-switched and packet mobile end systems are integrated, such that parts of the radio equipment are shared between circuit-switched and packet usage. A mobile end system will use a single radio channel to provide either switched circuit or packet communication, but cannot provide both simultaneously. When the radio channel is used for circuit-switched communication, packet communication services cannot be provided, and when the radio channel is used for packet communication, circuit-switched communication services cannot be provided. It is desired for a mobile end system to be able to receive switched circuit calls while monitoring a cellular packet data radio channel, and to transparently switch to switched circuit operation when an incoming call arrives, or when the use of switched circuit cellular equipment would provide superior performance or lower cost for the communications service. Current equipment cannot offer this service.
A variety of methods exist in prior art for providing reliable switched circuit data communication over cellular channels, as described in several U.S. Patents. These methods offer routing only within the context of the switched circuit network, including fixed and cellular subnetworks, and do not support interconnection of switched cellular data communication devices to packet data networks, or routing of packet data to mobile switched cellular data communications equipment. Reference is made in this regard to U.S. Pat. Nos. 5,159,592 granted to IBM and 4,837,800 granted to Motorola, Inc.